Most of my 38 years of flying has been at higher elevations, presently out of the Fort Collins/Greeley area, formerly out of Laramie. At higher elevations, you should not be using full rich for aerobatics, any more than you should use full rich for normal flight. You should be leaning on the ground for take off, and if you will be remaining within 2-3000' AGL for your aerobatics, I would recommend that you leave the mixture at your take-off setting. If you decide for safety reasons to be significantly higher, then I would recommend leaning for the lowest altitude you will be flying. For instance, if your "window" is from 8-10,000' MSL, lean for full power at 8,000 and then leave the mixture alone.
Caveat: I haven't instructed in more than 25 years, and I never instructed aerobatics. However, I learned aerobatics out of Boulder, and one of the airplanes I flew was a 150 hp fixed pitch Decathlon--the other was a 180 hp CS Super Decathlon. You will spend a lot of time at full power in a 115 hp Citabria, so your mixture needs to be rich enough to prevent engine damage but lean enough to give you full power. That will likely take a bit of experimenting to get exactly right, and without an engine analyzer, you probably can't. You might come close with an EGT. My method above will probably preserve your engine better than trying to adjust it "on the fly" for each maneuver.